Acquired hearing loss represents a complex interplay of genes and environment. Although there is much support for the existence of genes that influence the vulnerability of the cochlea to noise and ototoxins, few candidate genes or processes have been identified. One candidate process involves the generation and regulation of reactive oxygen species (ROS). Both chronic neurodegenerative disease and acute CNS injury involve elevated ROS, and deficiency of antioxidant enzymes promotes vulnerability to injury. We hypothesize that some genetic defects that predispose people to acquired hearing loss involve impairment of ROS regulatory mechanisms, rendering the cochlea more vulnerable to injury. We will apply hearing loss-prone and -resistant mouse models (C57BL/6, BALB/c, CBA/Ca), and 'knockout' mice deficient in antioxidant enzymes (superoxide dismutase and glutathione peroxidase), of carefully considered ages to the following Specific Aims: (1) Correlating the dynamics of cochlear ROS production following noise exposure with specific cochlear injury. We will establish the relation between the magnitude and time course of cochlear ROS production following acute noise exposure and cochlear injury, as measured by auditory brainstem responses, light and electron microscopy, and hair cell counts. (2) Identifying genetic influences on the relation between ROS production and noise-induced cochlear injury. We will determine the impact of genetic defects of hearing and ROS regulation on the relation between cochlear ROS production and noise-induced cochlear injury. (3) Uncovering the basis of genetic and age influences on the efficacy of antioxidants. We will determine the impact of age and genetic defects of hearing on the ability of exogenous antioxidants to attenuate both ROS production and noise-induced cochlear injury. Our experiments will establish how well the dynamics of ROS production predict cochlear injury, and whether progressive deafness genes may impair cochlear ROS regulation.